The present invention relates to improvements in delivery of fuel for combustion in kilns, boilers, and other applications where a controlled firing rate is used.
It has long been the practice to discard used tires as landfill, while only a relatively small portion of the available materials are reused. A great deal of recoverable chemical energy is therefore available for use by burning used pneumatic tires from motor vehicles, but such an energy source has not been recognized as it should be.
The combustion fuel value of scrap tires is relatively consistent for a given weight of material available to be burned. The toughness of tire material, however, particularly from fiber and wire-reinforced tires, has long made it difficult to use tires effectively as fuel. Machines are now available, however, which are capable of economically shredding tires into pieces small enough to be used efficiently as fuel in some applications.
For example, boiler furnaces which conventionally have burned chipped waste wood and bark known as hog fuel can readily accommodate shredded tires as a part of their fuel. In other applications, however, the conventional fuel, such oil, gas, or coal dust, is much more easily burned than has previously been possible with shredded tires, which will hereinafter at times be called tire-derived fuel. Previously there has been no available way to supply tire-derived fuel in well-controlled quantities to the combustion zone of a furnace or kiln to provide controllable amounts of thermal energy as a result of combustion.
Nevertheless, it is desirable in many applications to supplement or replace conventional oil, gas, or coal fuels by tire-derived fuel because of the savings which may be effected in the total fuel costs of operation.
As has been taught in Pennell U.S. Pat. No. 4,081,285 and Watson et al. U.S. Pat. No. 4,022,630, such devices as cement kilns can be fired effectively using low quality fuel such as household waste materials as a significant portion of the total mixture of fuels used, without the ash from such materials diminishing the quality of the cement produced thereby. This has been mentioned, as well, in the November 1983 issue of World Wastes magazine in an article entitled "Company Uses Refuse To Fuel Cement Works." Cement kilns and lime kilns can similarly utilize tire-derived fuel if it can be delivered to the combustion zones within such kilns conveniently and controllably. However, relatively inexpensive apparatus has not previously been available to enable the economical use of tire-derived fuel in such applications.
Besides tires, there are other wastes which are difficult to eliminate because of their toxicity and difficulty in handling them safely. Some organic chemical compounds cannot safely be dumped in landfills because of their carcinogenic properties, but can be rendered harmless by being exposed to high enough temperatures for a long enough time. Such temperatures and times are available in lime kilns and cement kilns, but the usual sludge form in which such chemical wastes are usually found cannot be dealt with efficiently using previously available technology.
What is needed, then, is apparatus and a method for measuring and delivering shredded tires and other comminuted refuse as fuel, particularly as a secondary fuel in applications where more expensive oil, gas, or coal is normally the primary source of chemical heat energy, and a way to burn chemical waste sludge to convert it to safe waste.